Glass antenna devices mounted on a vehicle window have been used widely to receive amplitude modulation waves or frequency modulation waves. Furthermore, glass antennas are beginning to be used as well as rod antennas for mobile communications (automobile telephones).
FIG. 8 shows a conventional antenna device 101 for automobile telephones (e.g. for an 800 MHz band). The antenna device 101 comprises antenna patterns 111 and 112 formed on a rear window glass 105, a coaxial cable 102, and a receiver transmitter (not shown).
The substantially linear radiation pattern 111 is connected to a core 121 that is the inner conductor of the coaxial cable 102. Furthermore, the ground pattern 112 is arranged so that its one edge becomes parallel to and in close proximity to the vehicle body 104, so that it can be coupled capacitively with the vehicle body 104. Furthermore, a braided wire that is the outer conductor of the coaxial cable is connected and fixed to the ground pattern with a presser metallic terminal 103. Thus, the antenna device is grounded to the vehicle body 104 via the ground pattern.
In such an antenna device, however, grounding by the ground pattern is not perfect. Thus, a potential difference may be generated between the ground pattern and the coaxial cable. With this potential difference, a current may flow from the ground pattern to the coaxial cable. This current causes radiation of waves from the coaxial cable. That is, the coaxial cable acts like an antenna.
Thus, in this antenna device, the antenna performance changes when the coaxial cable is turned around, that is the position of the coaxial cable is changed, as if the antenna itself is moved.
Accordingly, in this antenna device, it has been necessary to adjust the antenna taking the instability in the antenna performance due to the position of the coaxial cable into consideration. Thus, considerable time has been required to adjust such an antenna device entirely.
On the other hand, JP-A-6-53721 discloses a connecting structure of a glass antenna, particularly a structure in which the outer conductor of a coaxial cable is connected to a ring by soldering. JP-A-8-130404 also discloses another connecting structure of a glass antenna.
Because the outer conductor of the coaxial cable is connected to the ring by soldering, the glass antennas disclosed in the above-mentioned publications have good electrical connections.
However, even with this structure, the problem of generation of a potential difference between the ground pattern and the coaxial cable remains.
Moreover, positioning the coaxial cable in a vehicle may be restricted depending on the vehicle shape or the location at which the antenna device is mounted. The antenna performance may become poor with the turning that is allowed.